Metallic film variable resistor



to the method of making the same. sistors of the present invention areuseful either Patented Sept. 7, 1954 UNITED STATES PATENT OFFICEMETALLIC FILM VARIABLE RESISTOR Hubert W. Schleuning, Brooklyn, N. Y.,asslgnor to Polytechnic Institu te of Brooklyn, Brooklyn,

N. Y., a corporation of New York Application September 26, 1947, SerialNo. 776,323

7 Claims. (01. 201-55) This invention relates to variable resistors andThe reas potentiometers or as rheostats, or for any purpose requiringthe use of a resistor with a sliding contact.

An object of the invention is to devise a multitap resistor in which theresistance values between the different taps may be adjusted with greataccuracy and to any desired value within certain limits.

A further object of the invention is to devise a novel arrangement of aresistance element and a series of spaced contacts connected to theresistance element at different points along the length thereof.

The objects of my invention are accomplished by forming-the resistor ofa pair of contiguous, parallel bands of conductive material arranged ona dielectric carrier, one of the bands being of lowresistanceand forminga commutator for the movable contact, the other being of high resistanceand forming the resistance element of the resistor. The spaced contactsof the resistor are formed by segmenting the band of low resistance byforming transverse cuts through the band at spaced points along thelength thereof, thereby providing spaced contact segments of lowresistance connected to different linear sections of the band of highresistance. The resistance value between any pair of adjacent segmentsis controlled by extending'the transverse cut into the high resistanceband to the extent necessary to secure the desired valueof resistance.The two bands of resistance material may be formed as straight parallelbands, or they may be formed as concentric circular segmental bands.

The invention is illustrated in the accompanyingdrawing in which Figure1 is a plan view of one form of variable resistor in which theresistance element is formed of a linear band of thin metalilc filmdeposited on the elongated carrier plate,and the commutator segments orcontacts are formed from a linear band arranged along one edge of theresistance element;

Figure 2 is a section view of Figure 1 taken along the cutting line 2-2and shown on a greatly enlarged scale;

Figure 3 is a plan view of a second form of the invention in which thevariable resistor is constructed in circular form;

Figure 4 is a side elevational view of Figure 3 as seen from the right;

Figure 5 is a plan view of a masking plate or shield used in themanufacture of the arrangement shown in Figures 3 and 4; and

Figure 6 is an end view of Figure 5 as seen from the right.

Referring to Figures 1 and 2 of the drawing, numeral I indicates theinsulating carrier plate formed of glass or other suitable dielectricmaterial, and 2 is a band or strip of thin metallic film deposited onthe upper face of the plate I in any suitable manner but preferably bythermal evaporation in a Vacuum chamber. The thermal process ofdepositing metallic film is well known and need not be described indetail here. By using the process disclosed in the copending applicationof Weber et al., Serial No. 699,546, filed September 26, 1946 (nowPatent No. 2,586,752), the resulting films are atomically bonded to theglass and are very stable and rugged. The resistance film 2 may beformed over the entire width of the plate I, or it may cover a band ofless width than the plate. Preferably the film 2 is formed over theentire width of the plate and it extends over the length of the plateexcept for two end sections which are left bare. The value of theresistance of film 2 is controlled by the nature of the metal and bythickness of the film which is determined mainly by the duration of theevaporation process. The film may be formed from a pure metal or from analloy of metals such as Nichrome alloy. The film 2 may also be formed bybaking on a thin coating of a metal solution, such as a solution of aplatinumpalladium alloy in atomic percentages of to 50 percent platinumand 40 to 50 percent palladium. Such process is more fully disclosed inthe application of Weber et al., Serial No. 540,347, filed June 14, 1944(now Patent No. 2,529,436). A practical range for the total resistanceof band 2 is from ohms to 10,000 ohms or higher.

After the film 2 is deposited on the plate I, a low resistance band orstrip of metal 3 is deposited along one edge of the film 2 throughoutthe length of the film 2 and preferably lateral extensions 3a and 3bforming low-resistance terminal elements are provided at the ends of thefilm 2 extending entirely across the high resistance band. Twoconnection terminals 3a and 3b are provided at the ends of band 3. InFigure 2 the plate I and the films 2 and 3 are shown in sectionalelevation on a greatly enlarged scale. The metal band 3 may be formed byrepeated deposits by thermal evaporation, but I prefer to form this filmby painting on a coating of metal solution and then fixing or burning-inthe metallic film by the usual baking operation. I prefer to use aplatinum-gold alloy solution in forming band 3. It is necessary thatband 3 have contact 3 with band 2 along the length thereof but it is notnecessary that band 3 be formed entirely on resistance band 2. Also,low-resistance band 3 may be applied first and then the high resistanceband 2 may be applied to the carrier with one edge in contact with theband 3.

After the two film bands are deposited, spaced grooves 30 are formedacross the two films across the strip covered by band 3 to divide thelowresistance band into commutator segments as shown in Figure 2. Thismay be done by means of a diamond cutter operated either manually or bymachine. The separated segments of the metallic band 3 constitute spacedtap contacts connected to the resistance band 2 at spaced points alongthe length thereof. As will be seen in Figure 1, the grooves 30 areextended into the high resistance band 2 to a distance necessary toprovide the proper amount of resistance between adjacent contactelements. The desired amount of resistance between adjacent contacts maybe obtained by passing a known current between the two connectionterminals 30. and 3b and measuring the potential drop on opposite sidesof the out while it is being formed. The cutting is stopped as soon asthe potential difference reaches the desired value. The length of thecut determines the resistance between the contact segments on oppositesides of the cut as well as the resistance value between terminals 3aand 3b.

The resistor is provided with a slide bar 4 for supporting a slide 5having a resilient contact finger 5a (preferably formed of silver) whichengages the spaced contact segments formed in the band 3. The bar 4 issupported above the surface of the plate I by a pair of supportingstandards 4a and 4b mounted on the two bare end sections of plate 1. Aconnection terminal 51) is provided on one bare end section of plate Iand is connected to one of the supporting standards of bar 4.

In Figures 3 and 4 I have shown a construction in which the high and lowresistance metallic bands are arranged in circular form, and the slidingcontact is replaced by a rotary contact arm. In this arrangement theparts which serve the same function as corresponding parts in Figures 1and 2 are indicated by the same reference numerals. As will be seen, thecarrier plate I is of circular form and the two metallic bands 2 and 3are formed as concentric circular segments around the outer edge of theplate. The rotary contact arm 5a is supported on a rotary knob 5 whichis mounted at the center of the disc I by means of a screw 50 passingthrough a hole formed through the center of the circular plate I.

The resistance film 2 may be restricted to the desired part of the plateI by means of a mask or shield 6 shown in Figure 5. In this arrangementthe shield is formed of a plate of metal having two side flanges 6a and6b as shown in Figure 6, and is provided with an opening 60 formed of acircular segment of the same general shape as the resistance band 2 inFigure 3. The inner circular edge of the openin 60 will have the sameradius as the inner edge of the band 2 in Figure 3, but the outer edgeof the opening 60 should have a somewhat greater radius than the innerradius of the band 3 in Figure 3, so that the band 3 will overlap theouter edge of the resistance band 2 when applied to the disc I. Amounting screw I is secured to the plate 6 at the center of the opening6c and extends to the rear of the plate as shown in Figure 6. Thecarrier plate I is mounted on the screw 1 and is clamped against theback face of the plate 6 by means of a nut 8 bearing against the washer9. The masking shield B may be elongated and provided with a, number ofopenings 6c spaced along the length thereof to accommodate a number ofcarrier plates l at any given time. After the plates are mounted in theshield, one or more of such shields are placed within the vacuum chamberof the coating apparatus and the plates are exposed to the metal vaporthrough the openings to. It will be understood that only the exposedportions of the carrier plates I would be coated with the resistancefilm. After the plates are removed from the vacuum chamber, the lowresistance metal coating 3 may be applied to the outer portion of thedisc by painting on a suitable metal solution and then fixing the filmon the glass plate by the usual baking operation. As already explained,the low resistance band 3 may be applied first and then the highresistance film 2 applied with at least edge contact with band 3. Inthis case, when the high resistance film is applied through the openingin shield 6, the outer edge portion of the resistance film will overlapa portion of the low resistance band 3 which was previously applied.Also, the position of the two bands may be reversed if desired, that is,the band 2 may be formed outside of band 3.

It will be seen that my invention provides for the individual adjustmentof the resistance between each pair of adjacent contact segments, andthis feature is very useful for obtaining the desired relation betweenthe resistance values of difierent linear sections of the resistor. Itis obvious that by controlling the lengths of the cuts across the twometallic bands, the resistance values of successive sections may be madethe same or they may be caused to vary progressively or in any otherdesired manner from one end of the resistor to the other. Furthermore,the method of forming the contact segments makes it possible to form alarge number of segments in a small space or length. Also, it ispossible, by re-coating the resistance band, to change thecharacteristic of an already formed resistor.

I claim:

1. The method of forming a highly stable tapped resistor which consistsin depositing on one face of a glass plate a band of thin metallic filmby subjecting said plate to radiations from a source of vaporized metal,forming a second band of metallic film parallel with said first band andin contact with one edge thereof by depositing on said plate a film ofmetallic solution and burning-in said deposited film, said secondmetallic band having relatively low resistance value with respect tosaid first band, segmenting said low resistance band only along itslength by cutting transverse grooves therein at spaced points, andextending said grooves only partly into said thin metallic film toprovide a desired resistancedisplacement characteristic between thespaced face of a dielectric base, a pair of parallel contiguous bands ofmetallic film, one of said bands being relatively thin and having a highresistance value and the other being relatively thick and having a lowresistance value, said thin band being formed by subjecting said base toradiation from a source of vaporized metal in a vacuum space, said thickband being formed by depositing on said base a film of metallic solutionand burning-in said deposited film, and segmenting said thick band onlyby cutting transverse grooves thereacross at spaced points along itslength, whereby the segments of said thick band provide spacedlow-resistance contact members having contact With the continuoushighresistance band at different points along its length.

3. A tapped resistor comprising a base of dielectric material, a movablecontact mounted for movement along a predetermined path over the surfaceof said base, a low-resistance commutator band carried on said base andforming a track for said movable contact, said commutator band beingformed of a relatively thick metallic film bonded directly to thesurface of said base, said band being divided into commutator segmentsby spaced grooves cut transversely across said band at spaced pointsalong its length, and a resistance band carried by said base andcomprising a rela tively thin metallic film bonded directly to thesurface of said base and having a continuous linear portion arrangedparallel With said commutator band, portions of said thin metallic filmbeing on top of portions of said commutator segments, whereby saidsegments are connected to said resistance band at spaced points alongits length.

4, In an adjustable resistor device including a movable contact, aresistor element having a predetermined resistance-displacementcharacteristic comprising: a form of insulation material; alow-resistance film formed on and bonded to said form, said film beingsegmented to form a series of adjacent aligned insulated commutatorelements; and a thin high-resistance film formed directly on portions ofsaid commutator elements to form bridging connections between saidelements and being bonded to said elements and to said form, the exposedportions of said commutator elements serving as a commutator for amovable contact.

5. In an adjustable resistor device including a movable contact, aresistor element having a predetermined resistance-displacementcharacteristic comprising, a glass disc, an annular low-resistance filmformed on and bonded to said form, said film being segmented to form aseries of adjacent aligned insulated commutator elements, and a thinhigh-resistance film formed directly on portions of said commutatorelements and bonded thereto and to said form, the exposed portions ofsaid commutator elements serving as a commutator for a movable contact.

6. In an adjustable resistor device including a movable contact, aresistor element having a predetermined resistance-displacementcharacteristic comprising, a form of insulation material, alow-resistance film formed on and bonded to said form, said film beingsegmented to form a series of adjacent aligned insulated commutatorelements with unsegmented terminal portions, a thin high-resistance filmformed directly on portions of said commutator elements and bondedthereto and to said form, the exposed portions of said commutatorelements serving as a commutator for a movable contact, and a pair ofterminals individually bonded to said terminal portions.

7. In an adjustable resistor device including a movable contact, aresistor element having a predetermined resistance-displacementcharacteristic comprising, a form of insulation material, alow-resistance pure metallic film formed on and bonded to said form,said film being segmented to form a series of adjacent aligned insulatedcommutator elements, and a high-resistance pure metallic film formeddirectly on portions of said commutator elements and bonded thereto andto said form, the exposed portions of said commutator elements servingas a commutator for a movable contact.

Oct. 31, 1945.

